1. Field of the Invention
The present invention relates to a surface-discharge type display device used for image display or the like, and in particular relates to dielectrics in the display device.
2. Related Art
Among various types of color display devices used for displaying images on computers or televisions, surface-discharge type display devices which use plasma surface discharge processes, such as a PALC (plasma address liquid crystal) and a PDP (plasma display panel), have become a focus of attention as color display devices that enable large-size, slimline panels to be produced. Especially, expectations are running high for the commercialization of PDPs.
FIG. 1 is a partial perspective and sectional view of a conventional, typical PDP, whereas FIG. 2 is an expanded sectional view of part of the PDP shown in FIG. 1, looking at in a direction x.
In FIG. 1, a front glass substrate 11 and a back glass substrate 12 are set facing each other in parallel, with barrier ribs 19 being interposed in between. On the surface of the front glass substrate 11 facing the back glass substrate 12, a plurality of display electrodes 13 and a plurality of display scan electrodes 14 having a stripe shape (only two pairs of them are shown in FIG. 1, with each electrode being about 100 xcexcm in width and 5 xcexcm in thickness) are alternately aligned so as to be parallel to each other. The surface of the front glass substrate 11 on which the plurality of display electrodes 13 and the plurality of display scan electrodes 14 have been arranged is then coated with a dielectric layer 15 made of lead glass or the like to insulate each electrode, as shown in FIG. 2. The surface of the dielectric layer 15 is coated with a protective film 16 of magnesium oxide (MgO). This forms a front panel.
On the surface of the back glass substrate 12 facing the front glass substrate 11, a plurality of address electrodes 17 (only four of them are shown in FIG. 1) having a stripe shape are aligned in parallel to each other. The surface of the back glass substrate 12 on which the plurality of address electrodes 17 have been arranged is then coated with a dielectric layer 18 made of lead glass or the like. The barrier ribs 19 are formed between neighboring address electrodes 17. Lastly, phosphor layers 20R, 20G, and 20B in each of the three colors red (R), green (G), and blue (B) are applied to the gaps between neighboring barrier ribs 19 on the dielectric layer 18. This forms a back panel.
Discharge spaces 21 between the front panel and the back panel are filled with an inert gas. The areas within these discharges spaces 21 where the plurality of pairs of electrodes 13 and 14 intersect with the plurality of address electrodes 17 are cells for light emission.
To produce an image display on this PDP, a voltage equal to or greater than a discharge starting voltage is applied to display scan electrodes 14 and address electrodes 17 in cells which are to be illuminated, to induce an address discharge. After wall charges are accumulated on the inner wall of the MgO protective film 16, a pulse voltage is applied to each pair of display electrode 13 and display scan electrode 14 arranged on the same surface, to initiate a sustain discharge in the cells in which wall charges have been accumulated. Due to this sustain discharge, ultraviolet light is generated and excites phosphor layers 20R, 20G, and 20B, as a result of which visible light of the three primary colors red, green, and blue is generated and subjected to an additive process. Hence a full-color display is produced.
Here, the amount of current flowing through each of the display electrodes 13 and display scan electrodes 14 during the sustain discharge is known to be dependent on the capacitance of the dielectric layer 15. The dielectric layer 15 of lead glass, which is commonly used in the art, has a relative permittivity of 9 to 12, and therefore has a high capacitance. Accordingly, a large amount of current flows through each electrode during the sustain discharge, which increases the panel""s power consumption.
To overcome this problem, a technique of forming a dielectric layer from a material whose relative permittivity is 8 or lower has been proposed (see Japanese Laid-Open Patent Application H08-77930). According to this technique, the relative permittivity of the dielectric layer is decreased, so that the amount of current at the time of sustain discharge, and therefore the panel""s power consumption, can be reduced.
However, when the relative permittivity of the dielectric layer decreases, the capacitance of the dielectric layer decreases, too. If the capacitance is so low that sufficient wall charges cannot be accumulated in the cells which should be illuminated, sustain discharge may not be able to be induced, which results in a failure to fully illuminate the desired cells (hereafter referred to as xe2x80x9cillumination failurexe2x80x9d).
This problem is not confined to PDPs, but may occur in other surface-discharge type display devices such as PALCs that use similar surface discharge processes.
The present invention aims to provide a surface-discharge type display device that can reduce power consumption without causing illumination failures.
The above object can be fulfilled by a surface-discharge type display device including: a first panel including a first substrate and a plurality of electrode pairs which are aligned on a main surface of the first substrate and are each made up of a first electrode and a second electrode; and a second panel including a second substrate, a plurality of electrodes aligned on a main surface of the second substrate, and a plurality of barrier ribs aligned on the main surface of the second substrate, the second panel being placed parallel to the first panel with the plurality of barrier ribs being interposed in between, so that the plurality of electrodes face the plurality of electrode pairs, a discharge gas being enclosed in discharge spaces which are formed between the first panel and the second panel and are separated from each other by the plurality of barrier ribs, and the surface-discharge type display device producing an image display by using a surface discharge induced between the first and second electrodes, wherein the first and second electrodes are coated with a first dielectric layer, and an area that has a lower relative permittivity than the first dielectric layer is formed in an area surrounded on three sides by the first electrode, the second electrode, and the first substrate.
With this construction, sufficient wall charges are accumulated by the first dielectric layer. Also, since the relative permittivity between the first and second electrodes is low, the amount of current flowing at the time of sustain discharge is reduced. Hence the panel""s power consumption is reduced while suppressing the occurrence of illumination failures.
Such an area having a lower relative permittivity than the first dielectric layer may be formed by disposing a second dielectric layer having a lower relative permittivity than the first dielectric layer between the first and second electrodes. The formation of this second dielectric layer may be done using metal masking or nozzle injection.
Alternatively, the lower relative permittivity area may be formed by providing the first dielectric layer with a groove between the first and second electrodes in such a way that the bottom of the groove is closer to the first substrate than the surfaces of the first and second electrodes. Such a groove is filled with a discharge gas whose relative permittivity is about 1, so that the panel""s power consumption is reduced. Here, the first dielectric layer may be provided with a hollow instead of the groove. The formation of such a groove or hollow is done using sandblasting or a dielectric paste.
Furthermore, the aspect ratio which is the thickness-to-width ratio of each of the first and second electrodes may be in the range of 0.07 to 2.0. In so doing, not only the discharge spaces are widened but also the opening ratio of the panel is increased, which improves the panel""s luminous efficiency.
Thus, the surface-discharge type display device of the invention can reduce the power consumption without causing illumination failures during sustain discharge.